Friday, May 8, 2009

Gakken Kits: SX-150: Synthesizer Chronicle

SX-150 Synthesizer (3300 yen): Ok, I finally broke down and bought the synth. Actually, I've been wanting to get this kit for weeks, I was just waiting to reduce my "snack money for kits" debt, while also squeezing out as much remaining entertainment value as I could get from the other kits I already own. However, that opened me up to a rather rude shock. One Sunday, I'm in two different bookstores in Akihabara, looking at the synth kit mook to see what's required to add a 6V power adapter jack. The following Tuesday afternoon, the synth is sold out from both stores. Since I work Tuesday evenings, I didn't have time to try looking anywhere else, so I had to sit and wait. The next day, I go to another shop - also sold out. This place had an entire stack of the kits a few weeks earlier, and now, nothing. Which is a little strange, since the synth had only come out last August and it's going out of stock so quickly. But understandable since the smaller stores want to free up shelf space for selling the newest products. Anyway, I went into Kinokuniya in east Shinjuku, and they had two kits there - I bought both since my current plans are for using up to 3 kits on my homemade keyboard. Moral - buy what you need when you can (I'll get the third later if my plans work out).

(The kit, once it's assembled.)

The SX-150 is very similar to an analog synthesizer that PAiA Co. used to sell back in the 1980's (PAiA's still in business selling synth kits, but this one's not in their catalog anymore). It has a simple triangle wave/square wave generator, controls for Attack, Decay, Pitch and Cutoff, plus a reverb switch. There's an on-off switch, ext. source input and headphones output. The "keyboard" is a ceramic-like resistive strip and stylus. Where you put the stylus on the strip changes the output sound frequency. The case is heavy plastic, but the bottom plate is just a pre-punched piece of cardboard from the box the kit came in. The synth output is fairly limited as-is, being able to come close to a violin or a bass guitar, but mostly producing only sound effects suitable for 8-bit video games. The knobs and controls are flimsy, and the screw for holding on the bottom plate is too short to hold the plate in place (one of the knobs fell off when I was taking the kit apart, and it rolled somewhere so remote that I can no longer find it).

It's a very simple kit, compared to the rest of the Otona no Kagaku series - the case, 5 knobs, the resistive strip, the stylus, the circuit board with speaker pre-wired, and 8 screws. There's also a sheet of stickers if you want to fancy up the knobs and case. Even if you take your time and read the instructions carefully to ensure that you do everything right, it'll take less than 15 minutes to assemble it.

(I've got the 6V DC adapter jack added already. Next is the jack for the noise generator.)

My first mod was to add a jack for an external 6V DC power adapter. The second was my keyboard, and the third is a simple resistor string. The mook describes a mechanical sequencer (a hand-cranked drum with contacts to various resistive strips), a MIDI converter circuit, tactile bumps for use by the visually impaired, and how to make a wooden case and stylus. Youtube has a number of videos showing additional mods, like adding a piano-type keyboard, a push button bank, a larger resistive strip, a trill function and a noise generator. There's one video showing a variety of enhancements to the waveform circuits themselves. What I haven't seen yet, though, is a PC-driven digital controller to replace the ADSR volume controls. I may do that myself, eventually. I've already built the fingertip keyboard circuit and will upload a video of it to youtube when it's done (One of the relays seems to be bad and needs replacing, and I want to get enough knobs to put on all of the pots, too). I intend to make a second variation on the fingertip keyboard in a few weeks, and to add the noise generator mod.

(From the bottom, minus the cardboard cover plate.

The Ext. Source jack feeds an F/V circuit (which I'm assuming means Frequency to Voltage), so any input source that has a changing frequency can replace the resistive strip. The mook suggests connecting up the Theremin for this, but it's just as easy to plug in an MP3 player headphone jack (mono plug only), or to use Gakken's Poulson Wire Recorder. The point is that there's a lot of unexplored ideas for modding up the other Gakken kits to work in combination with the SX-150 (which I've already done for the Theremin).

(The full set-up (so far) - 2 synths, the keyboard, the relay and pots bank, and the theremin hooked up as an external input source. I've turned two pencils into fake drum sticks.)

The mook is a wonderful look into the history of synthesizers and the musicians that love them. There are various products from Moog, Roland, etc.; looks at Keith Emerson, Kraftwerk and Devo; and interviews with many Japanese musicians and engineers, including YMO (Yellow Magic Orchestra). There's a comparison between physical synthesizers and software versions. And, there's a description of a demo version of a software synth program called MT-1 (Music Track 1). ( And, if you needed suggestions, YMO offers settings for specific sounds for the SX-150 (electric guitar, ambulance siren, cat voice, and synth drums).

One of the guys mentioned in the mook has a few additional mods explained on his website. They include a couple variations on the ribbon controller, some changes to the waveform circuits, and an analog sequencer (same one shown in the mook).

(It's a little "rats-nesty", but I'll get some tie wraps for that later.)

Summary: Of all the Gakken Otona no Kagaku (Adult Science) kits, the SX-150 is the one most amenable to being modded. Out of the box, the sound range is very limited, thin and unsophisticated. There's no force control, so how hard you tap the resistive strip doesn't affect the sound out (unlike a piano key). But you can't expect much for 3000 yen (3300 including tax = $33 USD). Then again, with all of the mod suggestions, and possible sounds you can get when you're done, $33 is an incredible deal, even if you just look at the entertainment value for reading the mook and the time spent on experimenting with the kit. Sure, you can get better synths for just a few hundred dollars, but the little SX-150 is still a fun toy to play with. Get 3 - they're small. But only while supplies last.



I just got one of these in japantown, at a place called "new People" in San Francisco. I had read about it a few months ago, so when I saw it I just had to pick it up. One of the first mods I want to make is a 6v eternal power source like the one you made. How did you do it? would you mind helping me out? haha I have little experience with electronics so I decided that the sx-150 might be a good introduction for me.

TSOTE said...

If you haven't done much soldering before, then it'd be better if you contact me directly in e-mail. Basically, you'll want to go to an electronics parts store, like Radio Shack, and get a soldering iron, some extra solder if needed, a small spool of wire, a small wire cutter, and a 6 volt DC power adapter. Now, if you're not interested in doing that much soldering, just ask the clerk at the store for a jack that matches the plug on the power adapter. Otherwise, what I do is get a mono audio jack and plug, and replace the plug on the power supply with the audio plug. It's a little smaller, so it takes up a little less space, and it's easier to find at the stores. You'll also want to get a small, cheap voltmeter.

Pick a location on the case where the jack can fit without obstructions around it, and drill a hole in the case of the matching size. Make sure you leave yourself enough room around the plug to easily attach the wires. Mount the jack in the hole and solder about 3"-long wires to the connectors of the jack.

Depending on the type of jack you use, you'll either have 2 or 3 connectors. If it's two connectors, plug the power supply into the jack and use the volt meter to check which is the positive and which is the negative wire. Then unplug the power supply again. Strip a little insulation off the wires connected to the battery holder of the synth kit. Remove the batteries from the kit, and solder the positive wire from the jack to the positive connector of the battery holder. Solder the negative wire from the jack to the negative connector of the battery holder. Plug in the power adapter again and turn on the kit. When you have the power adapter connected, DO NOT put batteries in the kit (you'll damage the batteries).

If the kit doesn't turn on, TURN IT OFF IMMEDIATELY!!!

You either didn't solder the wires together with metal touching metal, you shorted the wires out, or you wired them backwards. Use the voltmeter to check whether you have a positive 6 volts at the battery holder connectors (that is, if you touch the red probe of the voltmeter to the red wire on the battery connector, and the black probe to the black wire of the battery connector, do you see the volt meter going to PLUS 6 V? If no, correct your wiring and try again.

If the battery jack has 3 wires, then you're going to need to do a little more work. Again, contact me directly in e-mail.

abedrous said...

hey there, wasn't sure what your email address was, as I stumbled on the blog through google.

I want to add the 6v ext power to my sx-150. Do I need to purchase an adapter with a specific amp rating?

TSOTE said...

Well, there's a link to my e-mail address up in the upper right corner of the blog in the "News" section, if you want it.

The SX-150 doesn't really draw that much, so any commercial 6V supply will be adequate. The one I found only went down to 2 amps, which is much more than I need, even with 2 synths and a bank of relays connected. But, being over-speced in this case doesn't cause any real problems. So, no, no specific amp rating. 500 mA or more should be fine.